Saving a document with password is indeed an encryption. The encryption methods are specified in the ODF Specification for encrypting the parts of the Zip package. (There is no ODF-specified encryption for the single- XML-file form of an ODF document.)
The default method, that works for all ODF 1.0/1.1/1.2 documents in packages (e.g., ODT, ODP, and ODS files), is by Password Based Key Derivation (PBKDF2) using HMAC and SHA1 starting with an SHA1 digest of the UTF-8 user-chosen password. The encryption with the derived key is Blowfish with 8-bit Cipher Feedback (8-bit CFB). This is done on each file of the Zip package that carries the parts of the ODF document. (Each part has a different, randomly-derived initialization vector, but the derived key is the same for all of them.) Starting with ODF 1.2, additional encryption methods can be chosen. However, there are interoperability issues if the document is intended to be opened with anything but the computer and software that was used to encrypt it (actually a common use case but not when secure interchange is intended). The fundamental weakness of the current approach is the use of human-entered passwords (which tend to be memorable and easily attackable), some well-known problems with information leakage from Zip files and known-/predictable-plaintext attacks. There is also a vulnerability if the password used is used anywhere else (e.g., for protecting fields in documents) such that its SHA1 digest becomes known or suspected. - Dennis -----Original Message----- From: Riccardo Bernardini [mailto:framefri...@gmail.com] Sent: Saturday, January 14, 2012 01:18 To: users@global.libreoffice.org Subject: [libreoffice-users] Encryption algorithms in Libre Office? Dear all, I apologize in advance if this is a FAQ, but I was not able to find an answer both in the FAQ page and in the first 4-5 pages of the mail archives (I searched for "password" and "encryption"). I know that Libre Office allows you to save a "password protected document," but I would like to know some more details about it. For example, is the document actually encrypted or simply Libre Office refuses to open it without the right password? (I expect [and hope] the former). If the former hypothesis is correct, which encryption algorithms are used? Thank you for any help. Riccardo -- For unsubscribe instructions e-mail to: users+h...@global.libreoffice.org Problems? http://www.libreoffice.org/get-help/mailing-lists/how-to-unsubscribe/ Posting guidelines + more: http://wiki.documentfoundation.org/Netiquette List archive: http://listarchives.libreoffice.org/global/users/ All messages sent to this list will be publicly archived and cannot be deleted -- For unsubscribe instructions e-mail to: users+h...@global.libreoffice.org Problems? http://www.libreoffice.org/get-help/mailing-lists/how-to-unsubscribe/ Posting guidelines + more: http://wiki.documentfoundation.org/Netiquette List archive: http://listarchives.libreoffice.org/global/users/ All messages sent to this list will be publicly archived and cannot be deleted
